/*
 * Copyright (c) 1994, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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 */

package java.io;

/**
 * This abstract class is the superclass of all classes representing
 * an input stream of bytes.
 *
 * <p> Applications that need to define a subclass of <code>InputStream</code>
 * must always provide a method that returns the next byte of input.
 *
 * @author Arthur van Hoff
 * @see java.io.BufferedInputStream
 * @see java.io.ByteArrayInputStream
 * @see java.io.DataInputStream
 * @see java.io.FilterInputStream
 * @see java.io.InputStream#read()
 * @see java.io.OutputStream
 * @see java.io.PushbackInputStream
 * @since JDK1.0
 */
public abstract class InputStream implements Closeable {

  // MAX_SKIP_BUFFER_SIZE is used to determine the maximum buffer size to
  // use when skipping.
  private static final int MAX_SKIP_BUFFER_SIZE = 2048;

  /**
   * Reads the next byte of data from the input stream. The value byte is
   * returned as an <code>int</code> in the range <code>0</code> to
   * <code>255</code>. If no byte is available because the end of the stream
   * has been reached, the value <code>-1</code> is returned. This method
   * blocks until input data is available, the end of the stream is detected,
   * or an exception is thrown.
   *
   * <p> A subclass must provide an implementation of this method.
   *
   * @return the next byte of data, or <code>-1</code> if the end of the stream is reached.
   * @throws IOException if an I/O error occurs.
   */
  public abstract int read() throws IOException;

  /**
   * Reads some number of bytes from the input stream and stores them into
   * the buffer array <code>b</code>. The number of bytes actually read is
   * returned as an integer.  This method blocks until input data is
   * available, end of file is detected, or an exception is thrown.
   *
   * <p> If the length of <code>b</code> is zero, then no bytes are read and
   * <code>0</code> is returned; otherwise, there is an attempt to read at
   * least one byte. If no byte is available because the stream is at the
   * end of the file, the value <code>-1</code> is returned; otherwise, at
   * least one byte is read and stored into <code>b</code>.
   *
   * <p> The first byte read is stored into element <code>b[0]</code>, the
   * next one into <code>b[1]</code>, and so on. The number of bytes read is,
   * at most, equal to the length of <code>b</code>. Let <i>k</i> be the
   * number of bytes actually read; these bytes will be stored in elements
   * <code>b[0]</code> through <code>b[</code><i>k</i><code>-1]</code>,
   * leaving elements <code>b[</code><i>k</i><code>]</code> through
   * <code>b[b.length-1]</code> unaffected.
   *
   * <p> The <code>read(b)</code> method for class <code>InputStream</code>
   * has the same effect as: <pre><code> read(b, 0, b.length) </code></pre>
   *
   * @param b the buffer into which the data is read.
   * @return the total number of bytes read into the buffer, or <code>-1</code> if there is no more
   * data because the end of the stream has been reached.
   * @throws IOException If the first byte cannot be read for any reason other than the end of the
   * file, if the input stream has been closed, or if some other I/O error occurs.
   * @throws NullPointerException if <code>b</code> is <code>null</code>.
   * @see java.io.InputStream#read(byte[], int, int)
   */
  public int read(byte b[]) throws IOException {
    return read(b, 0, b.length);
  }

  /**
   * Reads up to <code>len</code> bytes of data from the input stream into
   * an array of bytes.  An attempt is made to read as many as
   * <code>len</code> bytes, but a smaller number may be read.
   * The number of bytes actually read is returned as an integer.
   *
   * <p> This method blocks until input data is available, end of file is
   * detected, or an exception is thrown.
   *
   * <p> If <code>len</code> is zero, then no bytes are read and
   * <code>0</code> is returned; otherwise, there is an attempt to read at
   * least one byte. If no byte is available because the stream is at end of
   * file, the value <code>-1</code> is returned; otherwise, at least one
   * byte is read and stored into <code>b</code>.
   *
   * <p> The first byte read is stored into element <code>b[off]</code>, the
   * next one into <code>b[off+1]</code>, and so on. The number of bytes read
   * is, at most, equal to <code>len</code>. Let <i>k</i> be the number of
   * bytes actually read; these bytes will be stored in elements
   * <code>b[off]</code> through <code>b[off+</code><i>k</i><code>-1]</code>,
   * leaving elements <code>b[off+</code><i>k</i><code>]</code> through
   * <code>b[off+len-1]</code> unaffected.
   *
   * <p> In every case, elements <code>b[0]</code> through
   * <code>b[off]</code> and elements <code>b[off+len]</code> through
   * <code>b[b.length-1]</code> are unaffected.
   *
   * <p> The <code>read(b,</code> <code>off,</code> <code>len)</code> method
   * for class <code>InputStream</code> simply calls the method
   * <code>read()</code> repeatedly. If the first such call results in an
   * <code>IOException</code>, that exception is returned from the call to
   * the <code>read(b,</code> <code>off,</code> <code>len)</code> method.  If
   * any subsequent call to <code>read()</code> results in a
   * <code>IOException</code>, the exception is caught and treated as if it
   * were end of file; the bytes read up to that point are stored into
   * <code>b</code> and the number of bytes read before the exception
   * occurred is returned. The default implementation of this method blocks
   * until the requested amount of input data <code>len</code> has been read,
   * end of file is detected, or an exception is thrown. Subclasses are encouraged
   * to provide a more efficient implementation of this method.
   *
   * @param b the buffer into which the data is read.
   * @param off the start offset in array <code>b</code> at which the data is written.
   * @param len the maximum number of bytes to read.
   * @return the total number of bytes read into the buffer, or <code>-1</code> if there is no more
   * data because the end of the stream has been reached.
   * @throws IOException If the first byte cannot be read for any reason other than end of file, or
   * if the input stream has been closed, or if some other I/O error occurs.
   * @throws NullPointerException If <code>b</code> is <code>null</code>.
   * @throws IndexOutOfBoundsException If <code>off</code> is negative, <code>len</code> is
   * negative, or <code>len</code> is greater than <code>b.length - off</code>
   * @see java.io.InputStream#read()
   */
  public int read(byte b[], int off, int len) throws IOException {
    if (b == null) {
      throw new NullPointerException();
    } else if (off < 0 || len < 0 || len > b.length - off) {
      throw new IndexOutOfBoundsException();
    } else if (len == 0) {
      return 0;
    }

    int c = read();
    if (c == -1) {
      return -1;
    }
    b[off] = (byte) c;

    int i = 1;
    try {
      for (; i < len; i++) {
        c = read();
        if (c == -1) {
          break;
        }
        b[off + i] = (byte) c;
      }
    } catch (IOException ee) {
    }
    return i;
  }

  /**
   * Skips over and discards <code>n</code> bytes of data from this input
   * stream. The <code>skip</code> method may, for a variety of reasons, end
   * up skipping over some smaller number of bytes, possibly <code>0</code>.
   * This may result from any of a number of conditions; reaching end of file
   * before <code>n</code> bytes have been skipped is only one possibility.
   * The actual number of bytes skipped is returned. If {@code n} is
   * negative, the {@code skip} method for class {@code InputStream} always
   * returns 0, and no bytes are skipped. Subclasses may handle the negative
   * value differently.
   *
   * <p> The <code>skip</code> method of this class creates a
   * byte array and then repeatedly reads into it until <code>n</code> bytes
   * have been read or the end of the stream has been reached. Subclasses are
   * encouraged to provide a more efficient implementation of this method.
   * For instance, the implementation may depend on the ability to seek.
   *
   * @param n the number of bytes to be skipped.
   * @return the actual number of bytes skipped.
   * @throws IOException if the stream does not support seek, or if some other I/O error occurs.
   */
  public long skip(long n) throws IOException {

    long remaining = n;
    int nr;

    if (n <= 0) {
      return 0;
    }

    int size = (int) Math.min(MAX_SKIP_BUFFER_SIZE, remaining);
    byte[] skipBuffer = new byte[size];
    while (remaining > 0) {
      nr = read(skipBuffer, 0, (int) Math.min(size, remaining));
      if (nr < 0) {
        break;
      }
      remaining -= nr;
    }

    return n - remaining;
  }

  /**
   * Returns an estimate of the number of bytes that can be read (or
   * skipped over) from this input stream without blocking by the next
   * invocation of a method for this input stream. The next invocation
   * might be the same thread or another thread.  A single read or skip of this
   * many bytes will not block, but may read or skip fewer bytes.
   *
   * <p> Note that while some implementations of {@code InputStream} will return
   * the total number of bytes in the stream, many will not.  It is
   * never correct to use the return value of this method to allocate
   * a buffer intended to hold all data in this stream.
   *
   * <p> A subclass' implementation of this method may choose to throw an
   * {@link IOException} if this input stream has been closed by
   * invoking the {@link #close()} method.
   *
   * <p> The {@code available} method for class {@code InputStream} always
   * returns {@code 0}.
   *
   * <p> This method should be overridden by subclasses.
   *
   * @return an estimate of the number of bytes that can be read (or skipped over) from this input
   * stream without blocking or {@code 0} when it reaches the end of the input stream.
   * @throws IOException if an I/O error occurs.
   */
  public int available() throws IOException {
    return 0;
  }

  /**
   * Closes this input stream and releases any system resources associated
   * with the stream.
   *
   * <p> The <code>close</code> method of <code>InputStream</code> does
   * nothing.
   *
   * @throws IOException if an I/O error occurs.
   */
  public void close() throws IOException {
  }

  /**
   * Marks the current position in this input stream. A subsequent call to
   * the <code>reset</code> method repositions this stream at the last marked
   * position so that subsequent reads re-read the same bytes.
   *
   * <p> The <code>readlimit</code> arguments tells this input stream to
   * allow that many bytes to be read before the mark position gets
   * invalidated.
   *
   * <p> The general contract of <code>mark</code> is that, if the method
   * <code>markSupported</code> returns <code>true</code>, the stream somehow
   * remembers all the bytes read after the call to <code>mark</code> and
   * stands ready to supply those same bytes again if and whenever the method
   * <code>reset</code> is called.  However, the stream is not required to
   * remember any data at all if more than <code>readlimit</code> bytes are
   * read from the stream before <code>reset</code> is called.
   *
   * <p> Marking a closed stream should not have any effect on the stream.
   *
   * <p> The <code>mark</code> method of <code>InputStream</code> does
   * nothing.
   *
   * @param readlimit the maximum limit of bytes that can be read before the mark position becomes
   * invalid.
   * @see java.io.InputStream#reset()
   */
  public synchronized void mark(int readlimit) {
  }

  /**
   * Repositions this stream to the position at the time the
   * <code>mark</code> method was last called on this input stream.
   *
   * <p> The general contract of <code>reset</code> is:
   *
   * <ul>
   * <li> If the method <code>markSupported</code> returns
   * <code>true</code>, then:
   *
   * <ul><li> If the method <code>mark</code> has not been called since
   * the stream was created, or the number of bytes read from the stream
   * since <code>mark</code> was last called is larger than the argument
   * to <code>mark</code> at that last call, then an
   * <code>IOException</code> might be thrown.
   *
   * <li> If such an <code>IOException</code> is not thrown, then the
   * stream is reset to a state such that all the bytes read since the
   * most recent call to <code>mark</code> (or since the start of the
   * file, if <code>mark</code> has not been called) will be resupplied
   * to subsequent callers of the <code>read</code> method, followed by
   * any bytes that otherwise would have been the next input data as of
   * the time of the call to <code>reset</code>. </ul>
   *
   * <li> If the method <code>markSupported</code> returns
   * <code>false</code>, then:
   *
   * <ul><li> The call to <code>reset</code> may throw an
   * <code>IOException</code>.
   *
   * <li> If an <code>IOException</code> is not thrown, then the stream
   * is reset to a fixed state that depends on the particular type of the
   * input stream and how it was created. The bytes that will be supplied
   * to subsequent callers of the <code>read</code> method depend on the
   * particular type of the input stream. </ul></ul>
   *
   * <p>The method <code>reset</code> for class <code>InputStream</code>
   * does nothing except throw an <code>IOException</code>.
   *
   * @throws IOException if this stream has not been marked or if the mark has been invalidated.
   * @see java.io.InputStream#mark(int)
   * @see java.io.IOException
   */
  public synchronized void reset() throws IOException {
    throw new IOException("mark/reset not supported");
  }

  /**
   * Tests if this input stream supports the <code>mark</code> and
   * <code>reset</code> methods. Whether or not <code>mark</code> and
   * <code>reset</code> are supported is an invariant property of a
   * particular input stream instance. The <code>markSupported</code> method
   * of <code>InputStream</code> returns <code>false</code>.
   *
   * @return <code>true</code> if this stream instance supports the mark and reset methods;
   * <code>false</code> otherwise.
   * @see java.io.InputStream#mark(int)
   * @see java.io.InputStream#reset()
   */
  public boolean markSupported() {
    return false;
  }

}
